1. Field of the Invention
This invention relates to a cooling structure for cooling an electronic circuit package.
2. Description of the Related Art
Various structures have been proposed for a cooling structure for use for cooling an electronic circuit package mounted on a circuit board such as a printed circuit board and which generates a great amount of heat.
For example, a cooling structure wherein a piston is resiliently pressed against an integrated circuit by a spring to remove heat from the integrated circuit is disclosed in S. Oktay and H. C. Kammerer, "A Conduction-Cooled Module for High Performance LSI Device," IBM J. RES. DEVELOP, Vol. 26, No. 1, January, 1982. FIG. 1 shows the cooling structure by S. Oktay and H. C. Kammerer. A cold plate 47 in which coolant 48 circulates is provided. A hat 45 is mounted on the cold plate 47 with an intermediate layer 46 interposed therebetween. A spring 42 is accommodated in a cavity of the hat 45, and a piston 43 is mounted at an end of the spring 42. The piston 43 is resiliently pressed against the surface of an integrated circuit 41 by the resilient force of the spring 42. Helium (He) gas 44 is introduced around the integrated circuit 41 and in the cavity of the hat 45. Due to the construction of the cooling structure, heat generated from the integrated circuit 41 is transmitted to the piston 43 and then transmitted to the hat 45 by way of the helium gas 44, whereafter it is transmitted by way of the intermediate layer 46 and radiated to the coolant in the cold plate 47. In contrast, the example employs liquid coolant as the coolant 48 and also discloses a modified structure wherein a fin of a large size is provided in place of the cold plate 47 so as to effect forced air cooling.
In the cooling structure by S. Oktay et al., in order to follow up a fluctuation in height or tilt which occurs when the integrated circuit 41 is mounted on a circuit board, the surface of the piston 43 contacting the integrated circuit is formed as a spherical surface and a gap is provided between the hat 45 and piston 43. However, the spherical profile of the end of the piston and the provision of the gap between the piston and the hat result in a reduction of the effective heat transfer area and a reduction of the cooling performance.
Another cooling structure which makes use of a colliding jet of liquid coolant is disclosed in Japanese Patent Laid-Open Application No. 160150/1985 by Yamamoto et al. FIG. 2 shows the construction of the cooling structure by Yamamoto et al. A heat transfer substrate 52 is provided on the upper surface of an integrated circuit 51 mounted on a circuit board 50. A heat transfer plate 54 is mounted on the heat transfer substrate 52 with a deformable heat transfer member 53 interposed therebetween. Meanwhile, a cooling plate 56 is provided in an opposing relationship to the circuit board 50, and a nozzle 55 projecting from the cooling plate 56 is provided in an opposing relationship to the heat transfer plate 54. The nozzle 55 is provided to jet liquid coolant therefrom. The heat transfer plate 54 and the cooling plate 56 are connected to each other by means of bellows 57 so that coolant jetted from the nozzle 55 is all recovered to the cooling plate 56 side. Heat generated from the integrated circuit 51 is transmitted to the heat transfer plate 54 by way of the heat transfer substrate 52 and the heat transfer member 53. The heat transfer plate 54 is cooled by liquid coolant jetted from the nozzle 55. In the structure shown here, the heat transfer plate is cooled by a jet colliding therewith, and in order to raise the cooling capacity, it is necessary to either raise the flow velocity of the jet of coolant or increase the diameter of the nozzle to increase the flow rate. However, if the flow velocity is raised, the force applied to the integrated circuit increases and may possibly have a bad influence upon the reliability of the connection portion between the integrated circuit and the circuit board. Meanwhile, if the diameter of the nozzle is increased, since coolant flows radially after it collides with the heat transfer plate, a portion of the jet on the outer side portion of the nozzle is disturbed by a flow of another portion of the jet on the central portion of the nozzle after the jet collides with the heat transfer plate. Consequently, although the diameter of the nozzle is increased, there is no proportional rise in cooling capacity, and it is difficult to raise the performance of the entire structure.
In U.S. application Ser. No. 08/011,775, filed on Feb. 1, 1993 and assigned to the assignee of this application, a cooling structure suitable for using low boiling point coolant is disclosed, the disclosure of which is incorporated herein by reference. The cooling structure comprises a tubular fin member having many through-holes of small diameter, a flat plate member which is joined to and seals one end of the tubular fin member, a lid member attached to the end of the tubular fin member and a pipe member used as a nozzle from which coolant is jetted towards the plate member. The pipe member extends through the lid member. In the structure, coolant is supplied from the pipe member and flows out from the through-holes.